The present invention relates to a fluid friction clutch having a pot-shaped disk and a housing surrounding the pot disk (pot disk) while forming a working gap, the housing being pivotable with respect to the pot disk. At the wall of the housing opposite the circumference of the pot disk is a collecting groove for the return of clutch fluid from the work space into a storage chamber that is disposed axially in front of the work space. The collecting groove, via a controllable opening for the feeding of the clutch fluid, is connected with the work space, thread-type grooves for the feeding of the clutch fluid to the collecting groove being provided between the circumference of the pot disk and the adjacent housing.
A fluid friction clutch of the above-described type is shown in German Published Unexamined Patent Application No. 3,041,829. In the shown construction, the collecting groove is arranged at the end of the circumference of a pot disk facing the storage chamber and, via a retaining body projecting into it and having a connecting channel, is connected to the storage chamber. The thread-type grooves have such a slope that, when the pot disk is turned, the fluid located in the working gap between the housing and the circumference of the pot disk is transported to the collecting groove. The fluid is dammed up in this groove by the retaining body and is effectively returned into the storage chamber. The feeding of the clutch fluid into the work space takes place by means of a preferably temperature-dependently actuated valve lever that opens or closes an opening in the partition between the storage chamber and the work space.
A certain disadvantage of these constructions is the relatively costly manufacturing of the retaining body and its fitting into the collecting groove and into the housing. The tolerances that must be maintained for this purpose increase the manufacturing expenditures. For some uses, the switching behavior of the clutch is also too abrupt. The reason is that this type of construction causes a fast connecting and disconnecting of the clutch, which in some cases should be replaced by a more slowly connecting and disconnecting and thus more slowly operating clutch.
An object of the present invention is to provide a clutch of the initially mentioned type with an improved control behavior and especially a softer connecting and disconnecting.
This and other objects are achieved by providing in a fluid friction clutch of the initially mentioned type, a collecting channel disposed between groove sections that are axially adjacent on both sides of the channel and are sloped in opposite directions. By this development, clutch fluid, due to the relative rotation between the housing and the pot disk, and because of hydrodynamic phenomena, is transported to the collecting channel. As a result, a pressure rise is generated in the channel that is sufficient for causing the desired return of fluid into the storage chamber without having to provide a retaining body.
Opposed thread grooves at the circumference of a clutch disk of a fluid friction clutch are shown in U.S. Pat. No. 4,266,645. However, in that reference, the grooves are used only for distributing clutch fluid from a central feeding channel in the direction toward the ends of the circumference of the clutch disk and to transport it in the circulating system, and not for collecting clutch fluid and returning it into a storage chamber. That this is possible in an elegant manner and results in a number of advantages, is a finding of the present invention.
In a preferred embodiment of the present invention, the sections with the grooves are provided at the circumference of the pot disk and a recess is provided between these sections that forms a projection for the manufacturing tool for the grooves. If the collecting channel is placed in the center of the pot disk between equally large axial sections having grooves, and if the extent of the slope of the two opposed threads are equally large, a maximum pressure is generated in the collecting groove.
The arrangement of the sections having the thread-type grooves on the pot disk has advantages with respect to manufacturing technology. Additional tolerances for the installation of retaining bodies are not required. It is also contemplated, however, for the grooves to be provided at the interior wall of the housing. The pot disk may then, in a simple way, be developed as a deep-drawn part.
The new fluid friction clutch also has the advantage that it can operate with significantly less clutch fluid. This is a result of the fact that, because of the arrangement of the collecting channel in the center of the working gap, even the smallest amounts of oil are forced through a part of the working gap before they are pumped out again. The clutch therefore reacts to small amounts of clutch fluid which results in a soft connecting and disconnecting of the clutch. Because of this finely proportioned feeding of oil, stable intermediate speeds can also be maintained.
A further feature of preferred embodiments is that the return channel may also, in a very simple way, be provided in the housing. Since this can be cast, the return channel originating from the collecting channel may also be cast in so that a cutting process and a subsequent cleaning from chips is not required.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, an embodiment in accordance with the present invention.